This invention relates to a coating device and more particularly to a device for coating a condensed metal vapor onto a continuous web.
The coating of material by condensing a vapor thereon has long been known and such coatings have many uses. For example, printed wire circuit board is produced by depositing metal vapor on an element having a pattern defining means according to U.S. Pat. No. 2,948,261 to McGraw, Jr. Selenium rectifiers can be prepared by the coating of condensed selenium vapor such as is disclosed in U.S. Pat. No. 2,426,377 to Smith. Magnetic tape is produced by vapor deposition of magnetic material on a web according to U.S. Pat. No. 2,671,034 to Steinfeld. Condensed vapor deposition devices for the production of a variety of coatings are disclosed in U.S. Pat. No. 1,160,980, to Geer, U.S. Pat. No. 3,394,678 to Edwards et al., U.S. Pat. No. 2,440,135 to Alexander, U.S. Pat. No. 3,046,936 to Simons, Jr., U.S. Pat. No. 3,081,201 to Koller and U.S. Pat. No. 3,086,889 to Strong. In all such patents, the crucible employed does not provide direction of the vapor onto the substrate being coated.
More recently, there has been discovered a migration imaging method wherein a layer of particles are caused to migrate through a softenable layer in imagewise configuration. Such layer can be created by condensing metal vapor on the softenable layer by a process such as is disclosed in U.S. Pat. No. 3,598,644 to Goffe, et al., said patent hereby incorporated by reference.
Although uniformity of particle size and deposition on the substrate is desired in all cases, the formation of an imaging member for use in the migration imaging process is perhaps the most demanding with respect to such uniformity. Slight variations are detected by the quality of images produced by the imaging member which variations would perhaps not be detected in the coatings provided for other uses. The high temperature required for metal vaporization causes dimensional changes in the crucible and while such changes are small, the effects of such changes are sufficient to cause undesired variation in a layer employed in the migration imaging process.
Accordingly, when traditional vapor deposition systems are employed to provide migration imaging members, variations in the coating are detected as, for example, by measuring low blue light density (wratten filter No. 94) of the coating for a given white light density. This results in lowered image contrast in blue light. In addition, width uniformity of the coating varies intermittently. Thus, an improved means for coating is desired to provide highly uniform coatings particularly useful in migration imaging members.